System and method for retrieving related certificates

ABSTRACT

A system and method for searching and retrieving certificates, which may be used in the processing of encoded messages. In one embodiment, a certificate synchronization application is programmed to perform certificate searches by querying one or more certificate servers for all certificate authority (CA) certificates and cross-certificates on the certificate servers. In another embodiment, all certificates related to an identified certificate are retrieved from the certificate servers automatically by the certificate synchronization application, where the related certificates comprise at least one of one or more CA certificates and one or more cross-certificates. Embodiments of the invention facilitate at least partial automation of the downloading and establishment of certificate chains, thereby minimizing the need for users to manually search for individual certificates.

FIELD OF THE INVENTION

The invention relates generally to the processing of messages, such ase-mail messages, and more specifically to a system and method forsearching and retrieving certificates used in the processing of encodedmessages.

BACKGROUND OF THE INVENTION

Electronic mail (“e-mail”) messages may be encoded using one of a numberof known protocols. Some of these protocols, such as Secure MultipleInternet Mail Extensions (“S/MIME”) for example, rely on public andprivate encryption keys to provide confidentiality and integrity, and ona Public Key Infrastructure (PKI) to communicate information thatprovides authentication and authorization. Data encrypted using aprivate key of a private key/public key pair can only be decrypted usingthe corresponding public key of the pair, and vice-versa. Theauthenticity of public keys used in the encoding of messages isvalidated using certificates. In particular, if a user of a computingdevice wishes to encrypt a message before the message is sent to aparticular individual, the user will require a certificate for thatindividual. That certificate will typically comprise the public key ofthe individual, as well as other identification-related information.

If the requisite certificate for the intended recipient is not alreadystored on the user's computing device, the certificate must first beretrieved. Searching for and retrieving a certificate for a specificrecipient is a process that generally involves querying a certificateserver by having the user manually enter the name and/or e-mail addressof the intended recipient in a search form displayed on the computingdevice. Certificates located in the search are then temporarilydownloaded to the computing device for consideration, and a list oflocated certificates may be displayed to the user. Selected certificatesin the list may then be manually identified by a user for storage in anon-volatile store of the computing device, for potential future use.

Many organizations set up their own certificate servers that contain allof the certificates that have been issued to people in the organizationwho are able to send and receive encoded messages. If, for example, anindividual in one organization wishes to communicate with otherindividuals in another organization using encoded messages, thecertificates issued to those other individuals will need to be obtained.Furthermore, additional certificates may also be needed to verify theauthenticity or validity of the certificates issued to thoseindividuals. Manually searching for certificates, as they become needed,can be inconvenient and time-consuming. Manual searching forcertificates may be particularly cumbersome if the computing device onwhich the certificate searches are initiated is small in size (e.g. amobile device).

SUMMARY OF THE INVENTION

Embodiments of the invention are generally directed to a system andmethod for searching and retrieving certificates that automates at leastsome of the tasks typically performed manually by users in knowntechniques, and which may be employed by individuals within anorganization to more efficiently exchange encoded messages with otherindividuals in the organization that are able to do so. Morespecifically, embodiments of the invention may be employed to retrieverelated certificates from one or more certificate servers.

In one broad aspect of the invention, there is provided a method ofsearching and retrieving certificates comprising the steps of:performing a search on each of one or more certificate servers, whereinat least one query is submitted to the respective certificate server torequest retrieval of a plurality of certificates comprising at least oneof one or more certificate authority (CA) certificates and one or morecross-certificates stored thereon, wherein the search is performed by acertificate synchronization application; retrieving the plurality ofcertificates for storage on a computing device of a user; and storingthe plurality of certificates on the computing device.

In another broad aspect of the invention, there is provided a method ofsearching and retrieving certificates comprising the steps of:identifying a certificate at a computing device of a user; performing asearch on one or more certificate servers, wherein at least one query issubmitted to the one or more certificate servers to request retrieval ofa plurality of certificates comprising at least one of one or more CAcertificates and one or more cross-certificates related to theidentified certificate, wherein the search is performed by a certificatesynchronization application; retrieving the plurality of certificatesfor storage on a computing device of a user; and storing the pluralityof certificates on the computing device.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of embodiments of the invention, and to showmore clearly how it may be carried into effect, reference will now bemade, by way of example, to the accompanying drawings in which:

FIG. 1 is a block diagram of a mobile device in one exampleimplementation;

FIG. 2 is a block diagram of a communication subsystem component of themobile device of FIG. 1;

FIG. 3 is a block diagram of a node of a wireless network;

FIG. 4 is a block diagram illustrating components of a host system inone example configuration;

FIG. 5 is a block diagram showing an example of a certificate chain;

FIG. 6 is a block diagram illustrating components of an example of anencoded message;

FIG. 7A is a block diagram showing two example certificate chains;

FIG. 7B is a block diagram showing cross-certificates linking thecertificate chains of FIG. 7A;

FIG. 8A is a flowchart illustrating steps in a method of searching andretrieving certificates in an embodiment of the invention; and

FIG. 8B is a flowchart illustrating steps in a method of searching andretrieving certificates in another embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Some embodiments of the invention make use of a mobile station. A mobilestation is a two-way communication device with advanced datacommunication capabilities having the capability to communicate withother computer systems, and is also referred to herein generally as amobile device. A mobile device may also include the capability for voicecommunications. Depending on the functionality provided by a mobiledevice, it may be referred to as a data messaging device, a two-waypager, a cellular telephone with data messaging capabilities, a wirelessInternet appliance, or a data communication device (with or withouttelephony capabilities). A mobile device communicates with other devicesthrough a network of transceiver stations.

To aid the reader in understanding the structure of a mobile device andhow it communicates with other devices, reference is made to FIGS. 1through 3.

Referring first to FIG. 1, a block diagram of a mobile device in oneexample implementation is shown generally as 100. Mobile device 100comprises a number of components, the controlling component beingmicroprocessor 102. Microprocessor 102 controls the overall operation ofmobile device 100. Communication functions, including data and voicecommunications, are performed through communication subsystem 104.Communication subsystem 104 receives messages from and sends messages toa wireless network 200. In this example implementation of mobile device100, communication subsystem 104 is configured in accordance with theGlobal System for Mobile Communication (GSM) and General Packet RadioServices (GPRS) standards. The GSM/GPRS wireless network is usedworldwide and it is expected that these standards will be supersededeventually by Enhanced Data GSM Environment (EDGE) and Universal MobileTelecommunications Service (UMTS). New standards are still beingdefined, but it is believed that they will have similarities to thenetwork behaviour described herein, and it will also be understood bypersons skilled in the art that the invention is intended to use anyother suitable standards that are developed in the future. The wirelesslink connecting communication subsystem 104 with network 200 representsone or more different Radio Frequency (RF) channels, operating accordingto defined protocols specified for GSM/GPRS communications. With newernetwork protocols, these channels are capable of supporting both circuitswitched voice communications and packet switched data communications.

Although the wireless network associated with mobile device 100 is aGSM/GPRS wireless network in one example implementation of mobile device100, other wireless networks may also be associated with mobile device100 in variant implementations. Different types of wireless networksthat may be employed include, for example, data-centric wirelessnetworks, voice-centric wireless networks, and dual-mode networks thatcan support both voice and data communications over the same physicalbase stations. Combined dual-mode networks include, but are not limitedto, Code Division Multiple Access (CDMA) or CDMA2000 networks, GSM/GPRSnetworks (as mentioned above), and future third-generation (3G) networkslike EDGE and UMTS. Some older examples of data-centric networks includethe Mobitex™ Radio Network and the DataTAC™ Radio Network. Examples ofolder voice-centric data networks include Personal Communication Systems(PCS) networks like GSM and Time Division Multiple Access (TDMA)systems.

Microprocessor 102 also interacts with additional subsystems such as aRandom Access Memory (RAM) 106, flash memory 108, display 110, auxiliaryinput/output (I/O) subsystem 112, serial port 114, keyboard 116, speaker118, microphone 120, short-range communications 122 and other devices124.

Some of the subsystems of mobile device 100 performcommunication-related functions, whereas other subsystems may provide“resident” or on-device functions. By way of example, display 110 andkeyboard 116 may be used for both communication-related functions, suchas entering a text message for transmission over network 200, anddevice-resident functions such as a calculator or task list. Operatingsystem software used by microprocessor 102 is typically stored in apersistent store such as flash memory 108, which may alternatively be aread-only memory (ROM) or similar storage element (not shown). Thoseskilled in the art will appreciate that the operating system, specificdevice applications, or parts thereof, may be temporarily loaded into avolatile store such as RAM 106.

Mobile device 100 may send and receive communication signals overnetwork 200 after required network registration or activation procedureshave been completed. Network access is associated with a subscriber oruser of a mobile device 100. To identify a subscriber, mobile device 100requires a Subscriber Identity Module or “SIM” card 126 to be insertedin a SIM interface 128 in order to communicate with a network. SIM 126is one type of a conventional “smart card” used to identify a subscriberof mobile device 100 and to personalize the mobile device 100, amongother things. Without SIM 126, mobile device 100 is not fullyoperational for communication with network 200. By inserting SIM 126into SIM interface 128, a subscriber can access all subscribed services.Services could include: web browsing and messaging such as e-mail, voicemail, Short Message Service (SMS), and Multimedia Messaging Services(MMS). More advanced services may include: point of sale, field serviceand sales force automation. SIM 126 includes a processor and memory forstoring information. Once SIM 126 is inserted in SIM interface 128, itis coupled to microprocessor 102. In order to identify the subscriber,SIM 126 contains some user parameters such as an International MobileSubscriber Identity (IMSI). An advantage of using SIM 126 is that asubscriber is not necessarily bound by any single physical mobiledevice. SIM 126 may store additional subscriber information for a mobiledevice as well, including datebook (or calendar) information and recentcall information.

Mobile device 100 is a battery-powered device and includes a batteryinterface 132 for receiving one or more rechargeable batteries 130.Battery interface 132 is coupled to a regulator (not shown), whichassists battery 130 in providing power V+ to mobile device 100. Althoughcurrent technology makes use of a battery, future technologies such asmicro fuel cells may provide the power to mobile device 100.

Microprocessor 102, in addition to its operating system functions,enables execution of software applications on mobile device 100. A setof applications that control basic device operations, including data andvoice communication applications, will normally be installed on mobiledevice 100 during its manufacture. Another application that may beloaded onto mobile device 100 would be a personal information manager(PIM). A PIM has functionality to organize and manage data items ofinterest to a subscriber, such as, but not limited to, e-mail, calendarevents, voice mails, appointments, and task items. A PIM application hasthe ability to send and receive data items via wireless network 200. PIMdata items may be seamlessly integrated, synchronized, and updated viawireless network 200 with the mobile device subscriber's correspondingdata items stored and/or associated with a host computer system. Thisfunctionality creates a mirrored host computer on mobile device 100 withrespect to such items. This can be particularly advantageous where thehost computer system is the mobile device subscriber's office computersystem.

Additional applications may also be loaded onto mobile device 100through network 200, auxiliary I/O subsystem 112, serial port 114,short-range communications subsystem 122, or any other suitablesubsystem 124. This flexibility in application installation increasesthe functionality of mobile device 100 and may provide enhancedon-device functions, communication-related functions, or both. Forexample, secure communication applications may enable electroniccommerce functions and other such financial transactions to be performedusing mobile device 100.

Serial port 114 enables a subscriber to set preferences through anexternal device or software application and extends the capabilities ofmobile device 100 by providing for information or software downloads tomobile device 100 other than through a wireless communication network.The alternate download path may, for example, be used to load anencryption key onto mobile device 100 through a direct and thus reliableand trusted connection to provide secure device communication.

Short-range communications subsystem 122 provides for communicationbetween mobile device 100 and different systems or devices, without theuse of network 200. For example, subsystem 122 may include an infrareddevice and associated circuits and components for short-rangecommunication. Examples of short range communication would includestandards developed by the Infrared Data Association (IrDA), Bluetooth,and the 802.11 family of standards developed by IEEE.

In use, a received signal such as a text message, an e-mail message, orweb page download will be processed by communication subsystem 104 andinput to microprocessor 102. Microprocessor 102 will then process thereceived signal for output to display 110 or alternatively to auxiliaryI/O subsystem 112. A subscriber may also compose data items, such ase-mail messages, for example, using keyboard 116 in conjunction withdisplay 110 and possibly auxiliary I/O subsystem 112. Auxiliarysubsystem 112 may include devices such as: a touch screen, mouse, trackball, infrared fingerprint detector, or a roller wheel with dynamicbutton pressing capability. Keyboard 116 is an alphanumeric keyboardand/or telephone-type keypad. A composed item may be transmitted overnetwork 200 through communication subsystem 104.

For voice communications, the overall operation of mobile device 100 issubstantially similar, except that the received signals would be outputto speaker 118, and signals for transmission would be generated bymicrophone 120. Alternative voice or audio I/O subsystems, such as avoice message recording subsystem, may also be implemented on mobiledevice 100. Although voice or audio signal output is accomplishedprimarily through speaker 118, display 110 may also be used to provideadditional information such as the identity of a calling party, durationof a voice call, or other voice call related information.

Referring now to FIG. 2, a block diagram of the communication subsystemcomponent 104 of FIG. 1 is shown. Communication subsystem 104 comprisesa receiver 150, a transmitter 152, one or more embedded or internalantenna elements 154, 156, Local Oscillators (LOs) 158, and a processingmodule such as a Digital Signal Processor (DSP) 160.

The particular design of communication subsystem 104 is dependent uponthe network 200 in which mobile device 100 is intended to operate, thusit should be understood that the design illustrated in FIG. 2 servesonly as one example. Signals received by antenna 154 through network 200are input to receiver 150, which may perform such common receiverfunctions as signal amplification, frequency down conversion, filtering,channel selection, and analog-to-digital (A/D) conversion. A/Dconversion of a received signal allows more complex communicationfunctions such as demodulation and decoding to be performed in DSP 160.In a similar manner, signals to be transmitted are processed, includingmodulation and encoding, by DSP 160. These DSP-processed signals areinput to transmitter 152 for digital-to-analog (D/A) conversion,frequency up conversion, filtering, amplification and transmission overnetwork 200 via antenna 156. DSP 160 not only processes communicationsignals, but also provides for receiver and transmitter control. Forexample, the gains applied to communication signals in receiver 150 andtransmitter 152 may be adaptively controlled through automatic gaincontrol algorithms implemented in DSP 160.

The wireless link between mobile device 100 and a network 200 maycontain one or more different channels, typically different RF channels,and associated protocols used between mobile device 100 and network 200.A RF channel is a limited resource that must be conserved, typically dueto limits in overall bandwidth and limited battery power of mobiledevice 100.

When mobile device 100 is fully operational, transmitter 152 istypically keyed or turned on only when it is sending to network 200 andis otherwise turned off to conserve resources. Similarly, receiver 150is periodically turned off to conserve power until it is needed toreceive signals or information (if at all) during designated timeperiods.

Referring now to FIG. 3, a block diagram of a node of a wireless networkis shown as 202. In practice, network 200 comprises one or more nodes202. Mobile device 100 communicates with a node 202 within wirelessnetwork 200. In the example implementation of FIG. 3, node 202 isconfigured in accordance with General Packet Radio Service (GPRS) andGlobal Systems for Mobile (GSM) technologies. Node 202 includes a basestation controller (BSC) 204 with an associated tower station 206, aPacket Control Unit (PCU) 208 added for GPRS support in GSM, a MobileSwitching Center (MSC) 210, a Home Location Register (HLR) 212, aVisitor Location Registry (VLR) 214, a Serving GPRS Support Node (SGSN)216, a Gateway GPRS Support Node (GGSN) 218, and a Dynamic HostConfiguration Protocol (DHCP) 220. This list of components is not meantto be an exhaustive list of the components of every node 202 within aGSM/GPRS network, but rather a list of components that are commonly usedin communications through network 200.

In a GSM network, MSC 210 is coupled to BSC 204 and to a landlinenetwork, such as a Public Switched Telephone Network (PSTN) 222 tosatisfy circuit switched requirements. The connection through PCU 208,SGSN 216 and GGSN 218 to the public or private network (Internet) 224(also referred to herein generally as a shared network infrastructure)represents the data path for GPRS capable mobile devices. In a GSMnetwork extended with GPRS capabilities, BSC 204 also contains a PacketControl Unit (PCU) 208 that connects to SGSN 216 to controlsegmentation, radio channel allocation and to satisfy packet switchedrequirements. To track mobile device location and availability for bothcircuit switched and packet switched management, HLR 212 is sharedbetween MSC 210 and SGSN 216. Access to VLR 214 is controlled by MSC210.

Station 206 is a fixed transceiver station. Station 206 and BSC 204together form the fixed transceiver equipment. The fixed transceiverequipment provides wireless network coverage for a particular coveragearea commonly referred to as a “cell”. The fixed transceiver equipmenttransmits communication signals to and receives communication signalsfrom mobile devices within its cell via station 206. The fixedtransceiver equipment normally performs such functions as modulation andpossibly encoding and/or encryption of signals to be transmitted to themobile device in accordance with particular, usually predetermined,communication protocols and parameters, under control of its controller.The fixed transceiver equipment similarly demodulates and possiblydecodes and decrypts, if necessary, any communication signals receivedfrom mobile device 100 within its cell. Communication protocols andparameters may vary between different nodes. For example, one node mayemploy a different modulation scheme and operate at differentfrequencies than other nodes.

For all mobile devices 100 registered with a specific network, permanentconfiguration data such as a user profile is stored in HLR 212. HLR 212also contains location information for each registered mobile device andcan be queried to determine the current location of a mobile device. MSC210 is responsible for a group of location areas and stores the data ofthe mobile devices currently in its area of responsibility in VLR 214.Further VLR 214 also contains information on mobile devices that arevisiting other networks. The information in VLR 214 includes part of thepermanent mobile device data transmitted from HLR 212 to VLR 214 forfaster access. By moving additional information from a remote HLR 212node to VLR 214, the amount of traffic between these nodes can bereduced so that voice and data services can be provided with fasterresponse times and at the same time requiring less use of computingresources.

SGSN 216 and GGSN 218 are elements added for GPRS support; namely packetswitched data support, within GSM. SGSN 216 and MSC 210 have similarresponsibilities within wireless network 200 by keeping track of thelocation of each mobile device 100. SGSN 216 also performs securityfunctions and access control for data traffic on network 200. GGSN 218provides internetworking connections with external packet switchednetworks and connects to one or more SGSN's 216 via an Internet Protocol(IP) backbone network operated within the network 200. During normaloperations, a given mobile device 100 must perform a “GPRS Attach” toacquire an IP address and to access data services. This requirement isnot present in circuit switched voice channels as Integrated ServicesDigital Network (ISDN) addresses are used for routing incoming andoutgoing calls. Currently, all GPRS capable networks use private,dynamically assigned IP addresses, thus requiring a DHCP server 220connected to the GGSN 218. There are many mechanisms for dynamic IPassignment, including using a combination of a Remote AuthenticationDial-In User Service (RADIUS) server and DHCP server. Once the GPRSAttach is complete, a logical connection is established from a mobiledevice 100, through PCU 208, and SGSN 216 to an Access Point Node (APN)within GGSN 218. The APN represents a logical end of an IP tunnel thatcan either access direct Internet compatible services or private networkconnections. The APN also represents a security mechanism for network200, insofar as each mobile device 100 must be assigned to one or moreAPNs and mobile devices 100 cannot exchange data without firstperforming a GPRS Attach to an APN that it has been authorized to use.The APN may be considered to be similar to an Internet domain name suchas “myconnection.wireless.com”.

Once the GPRS Attach is complete, a tunnel is created and all traffic isexchanged within standard IP packets using any protocol that can besupported in IP packets. This includes tunneling methods such as IP overIP as in the case with some IPSecurity (Ipsec) connections used withVirtual Private Networks (VPN). These tunnels are also referred to asPacket Data Protocol (PDP) Contexts and there are a limited number ofthese available in the network 200. To maximize use of the PDP Contexts,network 200 will run an idle timer for each PDP Context to determine ifthere is a lack of activity. When a mobile device 100 is not using itsPDP Context, the PDP Context can be deallocated and the IP addressreturned to the IP address pool managed by DHCP server 220.

Referring now to FIG. 4, a block diagram illustrating components of ahost system in one example configuration is shown. Host system 250 willtypically be a corporate office or other local area network (LAN), butmay instead be a home office computer or some other private system, forexample, in variant implementations. In this example shown in FIG. 4,host system 250 is depicted as a LAN of an organization to which a userof mobile device 100 belongs.

LAN 250 comprises a number of network components connected to each otherby LAN connections 260. For instance, a user's desktop computer 262 awith an accompanying cradle 264 for the user's mobile device 100 issituated on LAN 250. Cradle 264 for mobile device 100 may be coupled tocomputer 262 a by a serial or a Universal Serial Bus (USB) connection,for example. Other user computers 262 b are also situated on LAN 250,and each may or may not be equipped with an accompanying cradle 264 fora mobile device. Cradle 264 facilitates the loading of information (e.g.PIM data, private symmetric encryption keys to facilitate securecommunications between mobile device 100 and LAN 250) from user computer262 a to mobile device 100, and may be particularly useful for bulkinformation updates often performed in initializing mobile device 100for use. The information downloaded to mobile device 100 may includecertificates used in the exchange of messages. It will be understood bypersons skilled in the art that user computers 262 a, 262 b willtypically be also connected to other peripheral devices not explicitlyshown in FIG. 4.

Embodiments of the invention relate generally to the processing ofmessages, such as e-mail messages, and some embodiments relate generallyto the communication of such messages to and from mobile device 100.Accordingly, only a subset of network components of LAN 250 are shown inFIG. 4 for ease of exposition, and it will be understood by personsskilled in the art that LAN 250 will comprise additional components notexplicitly shown in FIG. 4, for this example configuration. Moregenerally, LAN 250 may represent a smaller part of a larger network [notshown] of the organization, and may comprise different components and/orbe arranged in different topologies than that shown in the example ofFIG. 4.

In this example, mobile device 100 communicates with LAN 250 through anode 202 of wireless network 200 and a shared network infrastructure 224such as a service provider network or the public Internet. Access to LAN250 may be provided through one or more routers [not shown], andcomputing devices of LAN 250 may operate from behind a firewall or proxyserver 266.

In a variant implementation, LAN 250 comprises a wireless VPN router[not shown] to facilitate data exchange between the LAN 250 and mobiledevice 100. The concept of a wireless VPN router is new in the wirelessindustry and implies that a VPN connection can be established directlythrough a specific wireless network to mobile device 100. Thepossibility of using a wireless VPN router has only recently beenavailable and could be used when the new Internet Protocol (IP) Version6 (IPV6) arrives into IP-based wireless networks. This new protocol willprovide enough IP addresses to dedicate an IP address to every mobiledevice, making it possible to push information to a mobile device at anytime. An advantage of using a wireless VPN router is that it could be anoff-the-shelf VPN component, not requiring a separate wireless gatewayand separate wireless infrastructure to be used. A VPN connection wouldpreferably be a Transmission Control Protocol (TCP)/IP or User DatagramProtocol (UDP)/IP connection to deliver the messages directly to mobiledevice 100 in this variant implementation.

Messages intended for a user of mobile device 100 are initially receivedby a message server 268 of LAN 250. Such messages may originate from anyof a number of sources. For instance, a message may have been sent by asender from a computer 262 b within LAN 250, from a different mobiledevice [not shown] connected to wireless network 200 or to a differentwireless network, or from a different computing device or other devicecapable of sending messages, via the shared network infrastructure 224,and possibly through an application service provider (ASP) or Internetservice provider (ISP), for example.

Message server 268 typically acts as the primary interface for theexchange of messages, particularly e-mail messages, within theorganization and over the shared network infrastructure 224. Each userin the organization that has been set up to send and receive messages istypically associated with a user account managed by message server 268.One example of a message server 268 is a Microsoft Exchange™ Server. Insome implementations, LAN 250 may comprise multiple message servers 268.Message server 268 may also be adapted to provide additional functionsbeyond message management, including the management of data associatedwith calendars and task lists, for example.

When messages are received by message server 268, they are typicallystored in a message store [not explicitly shown], from which messagescan be subsequently retrieved and delivered to users. For instance, ane-mail client application operating on a user's computer 262 a mayrequest the e-mail messages associated with that user's account storedon message server 268. These messages would then typically be retrievedfrom message server 268 and stored locally on computer 262 a.

When operating mobile device 100, the user may wish to have e-mailmessages retrieved for delivery to the handheld. An e-mail clientapplication operating on mobile device 100 may also request messagesassociated with the user's account from message server 268. The e-mailclient may be configured (either by the user or by an administrator,possibly in accordance with an organization's information technology(IT) policy) to make this request at the direction of the user, at somepre-defined time interval, or upon the occurrence of some pre-definedevent. In some implementations, mobile device 100 is assigned its owne-mail address, and messages addressed specifically to mobile device 100are automatically redirected to mobile device 100 as they are receivedby message server 268.

To facilitate the wireless communication of messages and message-relateddata between mobile device 100 and components of LAN 250, a number ofwireless communications support components 270 may be provided. In thisexample implementation, wireless communications support components 270comprise a message management server 272, for example. Messagemanagement server 272 is used to specifically provide support for themanagement of messages, such as e-mail messages, that are to be handledby mobile devices. Generally, while messages are still stored on messageserver 268, message management server 272 can be used to control when,if, and how messages should be sent to mobile device 100. Messagemanagement server 272 also facilitates the handling of messages composedon mobile device 100, which are sent to message server 268 forsubsequent delivery.

For example, message management server 272 may: monitor the user's“mailbox” (e.g. the message store associated with the user's account onmessage server 268) for new e-mail messages; apply user-definablefilters to new messages to determine if and how the messages will berelayed to the user's mobile device 100; compress and encrypt newmessages (e.g. using an encryption technique such as Data EncryptionStandard (DES) or Triple DES) and push them to mobile device 100 via theshared network infrastructure 224 and wireless network 200; and receivemessages composed on mobile device 100 (e.g. encrypted using TripleDES), decrypt and decompress the composed messages, re-format thecomposed messages if desired so that they will appear to have originatedfrom the user's computer 262 a, and re-route the composed messages tomessage server 268 for delivery.

Certain properties or restrictions associated with messages that are tobe sent from and/or received by mobile device 100 can be defined (e.g.by an administrator in accordance with IT policy) and enforced bymessage management server 272. These may include whether mobile device100 may receive encrypted and/or signed messages, minimum encryption keysizes, whether outgoing messages must be encrypted and/or signed, andwhether copies of all secure messages sent from mobile device 100 are tobe sent to a pre-defined copy address, for example.

Message management server 272 may also be adapted to provide othercontrol functions, such as only pushing certain message information orpre-defined portions (e.g. “blocks”) of a message stored on messageserver 268 to mobile device 100. For example, when a message isinitially retrieved by mobile device 100 from message server 268,message management server 272 is adapted to push only the first part ofa message to mobile device 100, with the part being of a pre-definedsize (e.g. 2 KB). The user can then request more of the message, to bedelivered in similar-sized blocks by message management server 272 tomobile device 100, possibly up to a maximum pre-defined message size.

Accordingly, message management server 272 facilitates better controlover the type of data and the amount of data that is communicated tomobile device 100, and can help to minimize potential waste of bandwidthor other resources.

It will be understood by persons skilled in the art that messagemanagement server 272 need not be implemented on a separate physicalserver in LAN 250 or other network. For example, some or all of thefunctions associated with message management server 272 may beintegrated with message server 268, or some other server in LAN 250.Furthermore, LAN 250 may comprise multiple message management servers272, particularly in variant implementations where a large number ofmobile devices need to be supported.

Embodiments of the invention relate generally to the processing ofencoded messages, such as e-mail messages that are encrypted and/orsigned. While Simple Mail Transfer Protocol (SMTP), RFC822 headers, andMultipurpose Internet Mail Extensions (MIME) body parts may be used todefine the format of a typical e-mail message not requiring encoding,Secure/MIME (S/MIME), a version of the MIME protocol, may be used in thecommunication of encoded messages (i.e. in secure messagingapplications). S/MIME enables end-to-end authentication andconfidentiality, and protects data integrity and privacy from the timean originator of a message sends a message until it is decoded and readby the message recipient. Other known standards and protocols may beemployed to facilitate secure message communication, such as Pretty GoodPrivacy™ (PGP), OpenPGP, and others known in the art.

Secure messaging protocols such as S/MIME rely on public and privateencryption keys to provide confidentiality and integrity, and on aPublic Key Infrastructure (PKI) to communicate information that providesauthentication and authorization. Data encrypted using a private key ofa private key/public key pair can only be decrypted using thecorresponding public key of the pair, and vice-versa. Private keyinformation is never made public, whereas public key information isshared.

For example, if a sender wishes to send a message to a recipient inencrypted form, the recipient's public key is used to encrypt a message,which can then be decrypted only using the recipient's private key.Alternatively, in some encoding techniques, a one-time session key isgenerated and used to encrypt the body of a message, typically with asymmetric encryption technique (e.g. Triple DES). The session key isthen encrypted using the recipient's public key (e.g. with a public keyencryption algorithm such as RSA), which can then be decrypted onlyusing the recipient's private key. The decrypted session key can then beused to decrypt the message body. The message header may be used tospecify the particular encryption scheme that must be used to decryptthe message. Other encryption techniques based on public keycryptography may be used in variant implementations. However, in each ofthese cases, only the recipient's private key may be used to facilitatedecryption of the message, and in this way, the confidentiality ofmessages can be maintained.

As a further example, a sender may sign a message using a digitalsignature. A digital signature is a digest of the message (e.g. a hashof the message) encrypted using the sender's private key, which can thenbe appended to the outgoing message. To verify the signature of themessage when received, the recipient uses the same technique as thesender (e.g. using the same standard hash algorithm) to obtain a digestof the received message. The recipient also uses the sender's public keyto decrypt the digital signature, in order to obtain what should be amatching digest for the received message. If the digests of the receivedmessage do not match, this suggests that either the message content waschanged during transport and/or the message did not originate from thesender whose public key was used for verification. By verifying adigital signature in this way, authentication of the sender and messageintegrity can be maintained.

An encoded message may be encrypted, signed, or both encrypted andsigned. The authenticity of public keys used in these operations isvalidated using certificates. A certificate is a digital document issuedby a certificate authority (CA). Certificates are used to authenticatethe association between users and their public keys, and essentially,provides a level of trust in the authenticity of the users' public keys.Certificates contain information about the certificate holder, withcertificate contents typically formatted in accordance with an acceptedstandard (e.g. X.509).

Consider FIG. 5, in which an example certificate chain 300 is shown.Certificate 310 issued to “John Smith” is an example of a certificateissued to an individual, which may be referred to as an end entitycertificate. End entity certificate 310 typically identifies thecertificate holder 312 (i.e. John Smith in this example) and the issuerof the certificate 314, and includes a digital signature of the issuer316 and the certificate holder's public key 318. Certificate 310 willalso typically include other information and attributes that identifythe certificate holder (e.g. e-mail address, organization name,organizational unit name, location, etc.). When the individual composesa message to be sent to a recipient, it is customary to include thatindividual's certificate 300 with the message.

For a public key to be trusted, its issuing organization must betrusted. The relationship between a trusted CA and a user's public keycan be represented by a series of related certificates, also referred toas a certificate chain. The certificate chain can be followed todetermine the validity of a certificate.

For instance, in the example certificate chain 300 shown in FIG. 5, therecipient of a message purported to be sent by John Smith may wish toverify the trust status of certificate 310 attached to the receivedmessage. To verify the trust status of certificate 310 on a recipient'scomputing device (e.g. computer 262 a of FIG. 4) for example, thecertificate 320 of issuer ABC is obtained, and used to verify thatcertificate 310 was indeed signed by issuer ABC. Certificate 320 mayalready be stored in a certificate store on the computing device, or itmay need to be retrieved from a certificate source (e.g. LDAP server 284of FIG. 4 or some other public or private LDAP server). If certificate320 is already stored in the recipient's computing device and thecertificate has been designated as trusted by the recipient, thencertificate 310 is considered to be trusted since it chains to a stored,trusted certificate.

However, in the example shown in FIG. 5, certificate 330 is alsorequired to verify the trust of certificate 310. Certificate 330 isself-signed, and is referred to as a “root certificate”. Accordingly,certificate 320 may be referred to as an “intermediate certificate” incertificate chain 300; any given certificate chain to a rootcertificate, assuming a chain to the root certificate can be determinedfor a particular end entity certificate, may contain zero, one, ormultiple intermediate certificates. If certificate 330 is a rootcertificate issued by a trusted source (from a large certificateauthority such as Verisign or Entrust, for example), then certificate310 may be considered to be trusted since it chains to a trustedcertificate. The implication is that both the sender and the recipientof the message trust the source of the root certificate 330. If acertificate cannot be chained to a trusted certificate, the certificatemay be considered to be “not trusted”.

Certificate servers store information about certificates and listsidentifying certificates that have been revoked. These certificateservers can be accessed to obtain certificates and to verify certificateauthenticity and revocation status. For example, a Lightweight DirectoryAccess Protocol (LDAP) server may be used to obtain certificates, and anOnline Certificate Status Protocol (OCSP) server may be used to verifycertificate revocation status.

Standard e-mail security protocols typically facilitate secure messagetransmission between non-mobile computing devices (e.g. computers 262 a,262 b of FIG. 4; remote desktop devices). Referring again to FIG. 4, inorder that signed messages received from senders may be read from mobiledevice 100 and encrypted messages be sent to those senders, mobiledevice 100 is adapted to store certificates and associated public keysof other individuals. Certificates stored on a user's computer 262 awill typically be downloaded from computer 262 a to mobile device 100through cradle 264, for example.

Certificates stored on computer 262 a and downloaded to mobile device100 are not limited to certificates associated with individuals but mayalso include certificates issued to CAs, for example. Certaincertificates stored in computer 262 a and/or mobile device 100 can alsobe explicitly designated as “trusted” by the user. Accordingly, when acertificate is received by a user on mobile device 100, it can beverified on mobile device 100 by matching the certificate with onestored on mobile device 100 and designated as trusted, or otherwisedetermined to be chained to a trusted certificate.

Mobile device 100 may also be adapted to store the private key of thepublic key/private key pair associated with the user, so that the userof mobile device 100 can sign outgoing messages composed on mobiledevice 100, and decrypt messages sent to the user encrypted with theuser's public key. The private key may be downloaded to mobile device100 from the user's computer 262 a through cradle 264, for example. Theprivate key is preferably exchanged between the computer 262 a andmobile device 100 so that the user may share one identity and one methodfor accessing messages.

User computers 262 a, 262 b can obtain certificates from a number ofsources, for storage on computers 262 a, 262 b and/or mobile devices(e.g. mobile device 100). These certificate sources may be private (e.g.dedicated for use within an organization) or public, may reside locallyor remotely, and may be accessible from within an organization's privatenetwork or through the Internet, for example. In the example shown inFIG. 4, multiple PKI servers 280 associated with the organization resideon LAN 250. PKI servers 280 include a CA server 282 for issuingcertificates, an LDAP server 284 used to search for and downloadcertificates (e.g. for individuals within the organization), and an OCSPserver 286 used to verify the revocation status of certificates.

Certificates may be retrieved from LDAP server 284 by a user computer262 a, for example, to be downloaded to mobile device 100 via cradle264. However, in a variant implementation, LDAP server 284 may beaccessed directly (i.e. “over the air” in this context) by mobile device100, and mobile device 100 may search for and retrieve individualcertificates through a mobile data server 288. Similarly, mobile dataserver 288 may be adapted to allow mobile device 100 to directly queryOCSP server 286 to verify the revocation status of certificates.

In variant implementations, only selected PKI servers 280 may be madeaccessible to mobile devices (e.g. allowing certificates to bedownloaded only from a user's computer 262 a, 262 b, while allowing therevocation status of certificates to be checked from mobile device 100).

In variant implementations, certain PKI servers 280 may be madeaccessible only to mobile devices registered to particular users, asspecified by an IT administrator, possibly in accordance with an ITpolicy, for example.

Other sources of certificates [not shown] may include a Windowscertificate store, another secure certificate store on or outside LAN250, and smart cards, for example.

Referring now to FIG. 6, a block diagram illustrating components of anexample of an encoded message, as may be received by a message server(e.g. message server 268 of FIG. 4), is shown generally as 350. Encodedmessage 350 typically includes one or more of the following: a headerportion 352, an encoded body portion 354, optionally one or more encodedattachments 356, one or more encrypted session keys 358, and signatureand signature-related information 360. For example, header portion 352typically includes addressing information such as “To”, “From”, and “CC”addresses, and may also include message length indicators, and senderencryption and signature scheme identifiers, for example. Actual messagecontent normally includes a message body or data portion 354 andpossibly one or more attachments 356, which may be encrypted by thesender using a session key. If a session key was used, it is typicallyencrypted for each intended recipient using the respective public keyfor each recipient, and included in the message at 358. If the messagewas signed, a signature and signature-related information 360 are alsoincluded. This may include the sender's certificate, for example.

The format for an encoded message as shown in FIG. 6 is provided by wayof example only, and persons skilled in the art will understand thatembodiments of the invention will be applicable to encoded messages ofother formats. Depending on the specific messaging scheme used,components of an encoded message may appear in a different order thanshown in FIG. 6, and an encoded message may include fewer, additional,or different components, which may depend on whether the encoded messageis encrypted, signed or both.

Embodiments of the invention are generally directed to a system andmethod for searching and retrieving certificates that automates at leastsome of the tasks typically performed manually by users in knowntechniques for searching certificates, and provide means for relatedcertificates to be retrieved from one or more certificate servers.

For the purposes of this specification, two certificates are consideredto be related to each other if they can be used to form at least a partof the same certificate chain. An example of a certificate chain wasshown with reference to FIG. 5. As discussed with reference to FIG. 5, acertificate chain typically comprises root certificates, intermediatecertificates, and/or end entity certificates. A certificate chain can befollowed to determine the validity of a certificate, as may be formed toverify a signature on the certificate, or to check the trust status orrevocation status of the certificate, for example.

Many organizations establish their own CAs, which issue certificatesspecifically to individuals within their own organizations. End entitycertificates issued to individuals within a particular organization neednot be issued by a single CA associated with the organization. An endentity certificate is often issued by one of a number of subordinate orintermediate CAs within a CA hierarchy headed by a root CA for theorganization. This root CA may provide a self-signed root certificate tobe used as a “trust anchor”—a starting point for the validation ofcertificates issued within the organization.

Referring to FIG. 7A, a block diagram showing two example certificatechains is shown. The two example certificate chains are illustratedgenerally as 400 a and 400 b. It will be understood by persons skilledin the art that certificate chains 400 a and 400 b are provided asexamples. In particular, a certificate chain may comprise a fewer or agreater number of certificates than depicted in the examples shown.

Certificate chain 400 a depicts an example chain of certificates formedto validate a certificate 402 a issued to “user1”, an individual withinorganization “ABC”. Certificate 402 a chains to a self-signed rootcertificate 404 a, issued by a root CA of the organization and trustedby user1, via an intermediate certificate 406 a issued by the root CA toan intermediate CA of the organization. The certificates issued withinorganization ABC may be searched and retrieved from an LDAP servermaintained by the organization (e.g. LDAP server 284 of FIG. 4), forexample.

Similarly, certificate chain 400 b depicts an example chain ofcertificates formed to validate a certificate 402 b issued to “user2”,an individual within a different organization “XYZ”. Certificate 402 bchains to a self-signed root certificate 404 b issued by a root CA oforganization XYZ and trusted by user2, via an intermediate certificate406 b. The certificates issued within organization XYZ may be searchedand retrieved from an LDAP server maintained by organization XYZ, forexample.

Consider an example situation where user1 of organization ABC receivesan encoded message from user2 of organization XYZ. Even if user2 hasattached his certificate 402 b to the message, user1 will be unable toverify the trust status of user2's certificate 402 b with thatcertificate alone (assuming that user1 has not already stored user2'scertificate 402 b and marked it as trusted). If user1 does not trustcertificates from organization XYZ, then user2's certificate 402 bcannot be validated since it does not chain to a trusted certificate.

In order to facilitate secure communications between users of differentorganizations, it may be desirable to allow certificates to be used andtrusted between the organizations. An authentication method known ascross-certification may be performed between two organizations, where aCA of one organization certifies a CA of the other organization.

The term cross-certification may be used to refer generally to twooperations. The first operation, which is typically executed relativelyinfrequently, relates to the establishment of a trust relationshipbetween two CAs (e.g. across organizations or within the sameorganization), through the signing of one CA's public key by another CA,in a certificate referred to as a cross-certificate. The secondoperation, which is typically executed relatively frequently, involvesverifying a user's certificate through the formation of a certificatechain that includes at least one such cross-certificate.

Referring to FIG. 7B, a block diagram showing examples ofcross-certificates linking two example certificate chains is shown. Across-certificate 410 issued to the root CA of organization ABC by theroot CA of organization XYZ is shown in this example. Similarly, across-certificate 412 issued to the root CA of organization XYZ by theroot CA of organization ABC is shown.

The example of FIG. 7B illustrates mutual cross-certification betweentwo root CAs. However, other cross-certification methods are possible invariant implementations. For example, cross-certificates may be issuedby a subordinate CA in one organization to the root CA of anotherorganization. As a further example, a CA of a first organization mayissue a cross-certificate to a CA of a second organization, even if across-certificate is not issued back to the first organization by thesecond organization.

Furthermore, certificate usage across organizations may be restricted,as dictated by an organization's IT policy, for example. For instance,the IT policy of one organization may dictate that certificates fromother organizations will be trusted only for the purpose of processingencoded e-mail messages. Also, cross-certificates may be revoked by anissuing CA of one organization to terminate trust relationships withother organizations. This can facilitate more efficient control ofsecure e-mail communications between individuals across differentorganizations.

Cross-certificates facilitate secure communications between individualsof organizations that have established a trust relationship. Consideragain the situation where user1 of organization ABC receives an encodedmessage from user2 of organization XYZ. User1 will be able to verify thetrust status of user2's certificate 402 b, by retrieving certificates ina chain from user2's certificate 402 b, to root certificate 404 a issuedby a root CA of user1's organization and trusted by user1. Specifically,as shown in the example of FIG. 7B, the chain includes ABC's rootcertificate 404 a, cross-certificate 412, XYZ's root certificate 404 b,intermediate certificate 406 b, and user2's certificate 402 b.

For user1 to verify the trust status of user2's certificate 402 b, user1must obtain certificate 402 b. This will customarily accompany themessage from user2 to user1; however, in the event that certificate 402b is not provided and is not otherwise stored on user1's computingdevice, it must be retrieved, from an LDAP server maintained byorganization XYZ, or other certificate server, for example. Furthermore,each of the remaining certificates in the chain must also be retrievedto verify the trust status of certificate 402 b. The other certificatesin the chain, which in this example include a root certificate and across-certificate, would need to be retrieved from ABC's LDAP server,XYZ's LDAP server, or some other LDAP server accessible to user1.

Manually searching for and retrieving certificates to establish such acertificate chain can be a tedious, inconvenient task. This task can beparticularly cumbersome if the search for certificates needs to beinitiated by a user using a small device, such as a mobile device orother handheld device.

In some implementations of embodiments of the invention, a certificatesynchronization application is provided on a user's computing device.The certificate synchronization application is programmed to allow usersto initiate certificate searches of one or more certificate servers andretrieve related certificates on those certificate servers in accordancewith a method of an embodiment of the invention.

In one implementation, the certificate synchronization applicationexecutes and resides on a user's desktop computer (e.g. computer 262 aof FIG. 4) to which a cradle (e.g. cradle 264 of FIG. 4) for a mobiledevice (e.g. mobile device 100 of FIG. 4) is connected. However, invariant implementations, the certificate synchronization application mayexecute and reside on a desktop computer not equipped with a cradle fora mobile device, or on some other computing device. For example, thecertificate synchronization application may execute and reside on amobile device, which may have direct access to certificate servers (e.g.through mobile data server 288 of FIG. 4). By way of further example,the certificate synchronization application need not be executing on thesame computing device to which certificates would typically bedownloaded. For example, the certificate synchronization application mayexecute on a central server, such as a message management server thatsupports wireless devices (e.g. message management server 272 of FIG. 4)or an organization's message server (e.g. message server 268 of FIG. 4),for example. Moreover, the certificate synchronization application neednot be a stand-alone application, and the functions of the certificatesynchronization application described herein may be integrated with thefunctions of some other application, residing and executing on acomputing device such as a desktop computer, a mobile device, a messagemanagement server, a message server, or some other computing device.

Referring to FIG. 8A, a flowchart illustrating steps in a method ofsearching and retrieving certificates in an embodiment of the inventionis shown generally as 420. The method facilitates at least partialautomation of searching and retrieving certificates, to minimize theneed for a user to manually search for individual certificates stored onspecific certificate servers.

In one embodiment of the invention, at least some of the steps of themethod are performed by a certificate synchronization application thatexecutes and resides on a desktop computer. In variant embodiments, thecertificate synchronization application may be residing and executing ona computing device such as a mobile device, a message management server,a message server, or some other computing device.

At step 430, one or more certificate servers that will be used forcertificate searches are configured for access at the user's computingdevice. In one embodiment of the invention, at least one of theconfigured certificate servers is a remote server (e.g. a remote LDAPserver). For example, the remote server may be maintained by anorganization with which a trust relationship has been established by theuser's organization, where the remote server resides on a differentnetwork from the user's local network. Of the configured certificateservers, one or more certificate servers may be designated forcertificate searching.

Typically, information required to configure a certificate server mayinclude, for example, a host name, a host address or uniform resourcelocator (URL), a port number (e.g. for LDAP servers), a default basequery, a query limit, and/or an indication of whether certificateinformation is to be compressed for transmission. In one implementation,such configuration information can be input by a user, and defaultvalues for certain inputs may be set in the certificate synchronizationapplication. In other implementations, such configuration informationmay be defined by the certificate synchronization application, andpossibly pre-defined by an IT administrator in accordance with an ITpolicy. Still other implementations may permit some configurationinformation to be input or modified by users, while not permitting otherconfiguration information to be user-modified.

Similarly, in one implementation, the certificate synchronizationapplication may permit users to manually designate specific certificateservers that will be queried and searched in accordance with anembodiment of the invention. In other implementations, the certificatesynchronization application may automatically designate specificcertificate servers to be searched, possibly as directed by an ITadministrator in accordance with an IT policy. Still otherimplementations may permit some degree of user configuration, byallowing a user to designate specific certificate servers but only froma set defined by an IT administrator, in accordance with an IT policy,for example.

At step 440, a request is received by the certificate synchronizationapplication to initiate a search for all CA certificates andcross-certificates in the servers designated at step 430. For example,the request may be received from the user. As a further example, in thecase where the certificate synchronization application resides andexecutes on a computer such as a desktop computer to which a mobiledevice can be connected, the request may be initiated automatically whenthe device is connected (e.g. via cradle 264 of FIG. 4) to the computer.

At step 450, the certificate synchronization application searches forcertificates by automatically querying each designated certificateserver, to locate for retrieval all of the CA certificates andcross-certificates stored on each server. Queries are automaticallyconstructed by the certificate synchronization application to locatecertificates having set attributes that identify certificates as beingCA certificates, which will typically include both intermediatecertificates and root certificates. Similarly, queries are automaticallyconstructed by the certificate synchronization application to locatecertificates having set attributes that identify certificates as beingcross-certificates. In some implementations, certain certificate serverswill accept queries employing some blank or “wild card” type searchindicators for use in appropriate fields that would facilitate suchsearching.

At step 460, the located CA certificates and cross-certificatesresulting from the searches of the designated certificate servers aredownloaded to the computing device, and stored in a certificate store onthe computing device for future use. Duplicate certificates may befiltered out before storage in the certificate store.

Accordingly, a pool of CA certificates and cross-certificates is madeavailable on the computing device, so that when an end entitycertificate is to be validated on the computing device, there will be agreater likelihood that an entire certificate chain can be establishedwithout the need to search for additional certificates.

In one embodiment, the computing device upon which the retrievedcertificates are stored is a computer to which a mobile device can beconnected. In that embodiment, at a subsequent point in time, at step470, the user may select one or more end entity certificates to bedownloaded from the computing device to the mobile device. For example,the user may select an end entity certificate of an individual with whomhe expects to communicate encoded messages with through his mobiledevice.

At step 480, the certificate synchronization application determines andlocates CA certificates and/or cross-certificates in the certificatestore on the computing device that are related to the end entitycertificate(s) selected at step 470, and downloads the selected endentity certificate(s) and related CA certificates and/orcross-certificates to the mobile device. These downloaded certificatesmay then be stored in a certificate store on the mobile device.

By pre-loading CA certificates and cross-certificates on a computingdevice that may be related to end entity certificates that a user maywish to download to his mobile device, and subsequently downloadingrelated pre-loaded certificates to the mobile device, the likelihoodthat a complete chain of certificates may be formed when it is necessaryto verify a particular end entity certificate on the mobile device willbe increased. As a result, the likelihood that a user of the mobiledevice will need to manually initiate searches for certificates (e.g.root and intermediate CA certificates and cross-certificates) tocomplete a certificate chain will be decreased.

Referring now to FIG. 8B, a flowchart illustrating steps in a method ofsearching and retrieving certificates in another embodiment of theinvention is shown generally as 500. The method also facilitates atleast partial automation of searching and retrieving certificates, tominimize the need for a user to manually search for individualcertificates stored on specific certificate servers.

In one embodiment of the invention, at least some of the steps of themethod are performed by a certificate synchronization application thatexecutes and resides on a desktop computer. In variant embodiments, thecertificate synchronization application may be residing and executing ona computing device such as a mobile device, a message management server,a message server, or some other computing device.

At step 510, one or more end entity certificates are identified, so thatcertificates related to each identified end entity certificate may beretrieved in subsequent steps of the method.

In one embodiment, an end entity certificate is automatically identifiedby the certificate synchronization application when a request is made bya user to retrieve a specific end entity certificate from a certificateserver (e.g. an LDAP server), as shown at step 520. The request isinitiated from the user's computing device, which may be the user'sdesktop computer or mobile device, for example.

In a variant embodiment, the user may already be in possession of aspecific end entity certificate (in which case, the certificate may notneed to be retrieved again at step 520), and the certificate may beidentified through manual selection of a user wishing to downloadrelated certificates.

In a variant embodiment, an end entity certificate is automaticallyidentified by the certificate synchronization application by selecting acertificate that is received by a user, in an incoming message, forexample. In this way, the certificate synchronization applicationanticipates that the user may need related certificates to verify thecertificate received with the incoming message. Other predictivealgorithms may be applied by the certificate synchronization applicationto identify end entity certificates in variant embodiments.

At step 530, one or more certificate servers that will be used forcertificate searches are configured and designated for access at theuser's computing device. In one embodiment, at least one of theconfigured and designated certificate servers is a remote server, asdescribed at step 430 of FIG. 8A. The remote server may comprise anidentified end entity certificate and/or at least some of thecertificates related thereto. For example, the remote server may be anLDAP server maintained by an organization to which the sender of amessage received by the user belongs.

At step 540, a search for all certificates related to the identified endentity certificate is initiated by the certificate synchronizationapplication.

At step 550, the certificate synchronization application searches forcertificates by executing a search algorithm, in which the designatedcertificate servers are queried to locate for retrieval any CAcertificates and cross-certificates specifically related to eachidentified end entity certificate. For example, a query may beautomatically constructed by the certificate synchronization applicationto locate the CA certificate of the CA that issued an identified endentity certificate. Successive queries are then automaticallyconstructed to find further certificates in the chain, preferably untila root CA certificate is obtained. The further certificates can includeCA certificates and cross-certificates, for example.

At step 560, the certificates located at step 550 resulting from thesearches of the designated certificate servers are downloaded to theuser's computing device. In one embodiment, the downloaded certificatesare stored in a certificate store on the computing device for futureuse. Duplicate certificates may be filtered out at this step beforestorage in the certificate store.

In one embodiment, the computing device is a computer, and the chain ofrelated certificates may be downloaded to a mobile device coupled to thecomputer at step 570 (e.g. through a physical connection to thecomputer), for use on the mobile device. The certificates downloaded tothe mobile device are stored in a certificate store on the mobiledevice.

By downloading related certificates to the mobile device, the likelihoodthat a user of the mobile device will need to manually initiate searchesfor certificates on the mobile device to complete a certificate chainwill be decreased.

While the foregoing method makes reference to the identification of anend entity certificate for which related certificates are to beretrieved, in variant embodiments, the identified certificate may be anintermediate or root certificate for which related certificates are tobe retrieved.

In variant embodiments of the invention, the certificate synchronizationapplication may execute on a mobile device or a central server, forexample, and is adapted to retrieve related certificates and forwardthem directly to a mobile device, without first downloading or storingthe related certificates to a user's computer, for example.

The steps of a method of searching and retrieving certificates inembodiments of the invention may be provided as executable softwareinstructions stored on computer-readable media, which may includetransmission-type media.

The invention has been described with regard to a number of embodiments.However, it will be understood by persons skilled in the art that othervariants and modifications may be made without departing from the scopeof the invention as defined in the claims appended hereto.

1. A method of searching and retrieving certificates comprising thesteps of: a) performing a search on each of one or more certificateservers, wherein at least one query is submitted to the respectivecertificate server to request retrieval of a plurality of certificatescomprising at least one of one or more CA certificates and one or morecross-certificates stored thereon, wherein the search is performed by acertificate synchronization application; b) retrieving the plurality ofcertificates for storage on a computing device of a user; and c) storingthe plurality of certificates on the computing device.
 2. The method ofclaim 1, wherein the plurality of certificates comprises all of the CAcertificates and cross-certificates stored on the respective certificateserver.
 3. The method of claim 1, wherein the certificatesynchronization application executes and resides on the computingdevice.
 4. The method of claim 1, wherein at least one of thecertificate servers is a server remote to the user.
 5. The method ofclaim 4, wherein the remote server is an LDAP server.
 6. The method ofclaim 1, wherein the computing device is a mobile device.
 7. The methodof claim 1, further comprising the steps of: selecting at least one endentity certificate, identifying certificates related to each of the atleast one end entity certificates from the plurality of certificatesstored on the at least one computing device, and downloading the relatedcertificates to a mobile device coupled to the computing device.
 8. Asoftware application for execution on a computing device, theapplication comprising a plurality of instructions stored on acomputer-readable medium, the instructions for the method of searchingand retrieving certificates as claimed in claim
 1. 9. A system forsearching and retrieving certificates comprising at least one computingdevice, wherein a certificate synchronization application executes andresides on a computing device of the at least one computing device,wherein the certificate synchronization application is programmed toperform steps of the method of searching and retrieving certificates asclaimed in claim
 1. 10. A method of searching and retrievingcertificates comprising the steps of: a) identifying a certificate at acomputing device of a user; b) performing a search on one or morecertificate servers, wherein at least one query is submitted to the oneor more certificate servers to request retrieval of a plurality ofcertificates comprising at least one of one or more CA certificates andone or more cross-certificates related to the identified certificate,wherein the search is performed by a certificate synchronizationapplication; c) retrieving the plurality of certificates for storage ona computing device of a user; and d) storing the plurality ofcertificates on the computing device.
 11. The method of claim 10,wherein the plurality of certificates comprises all of the CAcertificates and cross-certificates related to the identifiedcertificate stored on the one or more certificate servers.
 12. Themethod of claim 10, wherein the identified certificate is an end entitycertificate.
 13. The method of claim 10, wherein the certificatesynchronization application executes and resides on the computingdevice.
 14. The method of claim 10, wherein at least one of thecertificate servers is a server remote to the user.
 15. The method ofclaim 14, wherein the remote server is an LDAP server.
 16. The method ofclaim 10, wherein the computing device is a mobile device.
 17. Themethod of claim 10, further comprising the step of downloading theplurality of certificates to a mobile device coupled to the computingdevice.
 18. The method of claim 10, further comprising the step ofrequesting a specified certificate from a certificate server, andwherein the specified certificate is the certificate identified at stepa).
 19. The method of claim 10, further comprising the step of receivinga certificate with a message for the user, and wherein the receivedcertificate is the certificate identified at step a).
 20. A softwareapplication for execution on a computing device, the applicationcomprising a plurality of instructions stored on a computer-readablemedium, the instructions for the method of searching and retrievingcertificates as claimed in claim
 10. 21. A system for searching andretrieving certificates comprising at least one computing device,wherein a certificate synchronization application executes and resideson a computing device of the at least one computing device, wherein thecertificate synchronization application is programmed to perform stepsof the method of searching and retrieving certificates as claimed inclaim 10.